REPORT OF THE DIRECTOR IQII I/I 



formed by the action of circulating solutions, which either con- 

 centrated into large masses, pyrite already present in a disseminated 

 condition in the rocks, or introduced the mineral from an outside 

 source. Manifestly these two sources of pyrite are in no way 

 antagonistic and may both be of importance. Nor is it necessary 

 to suppose that the pyrite is derived directly from iron sulfid 

 of either origin, since it may, in part or wholly, result from re- 

 actions converting totally different compounds into sulfid. 



All of the phenomena point to conditions quite different from 

 those prevailing during metamorphism, involving the destruction of 

 metamorphic minerals, but still, doubtless at such depth as to give 

 temperatures and pressures considerably above those at the surface, 

 and wath circulating hot water, either magmatic or meteoric, as the 

 active transporting agent. Between these two sources of the solu- 

 tions there is no w^ay of deciding finally, since solutions of either 

 origin would probably be capable of effecting all the changes 

 observed in connection with ore formation. Of minerals pointing 

 certainly to igneous sources, only tourmalin is frequent in the ores, 

 and this antedates much of the pyrite. Still, the mineral alterations 

 in the rocks and ores are such as to suggest, strongly, the work of 

 magmatic waters and, this being the case, with igneous intrusions 

 so abundant throughout the region it is probable that magmatic 

 solutions played a major part in the processes of ore concentration. 



A formation that has been so thoroughly injected by igneous rocks 

 and soaked by magmatic solutions and vapors might naturally be 

 expected to show much concentration of metaliferous materials, and 

 the probable explanation of their comparative scarcity is to be 

 found in the fact that the existing surface rocks were, at the time 

 of these activities under heavy cover, up into which the more 

 mobile elements were carried to be subsequently removed by erosion, 

 leaving the more abundant and stable substances, chiefly iron com- 

 pounds, in the deeper regions now exposed. In so far as the pyrite 

 is of sedimentary origin, it is probable that its migration and con- 

 centration may have been in part due to these magmatic -agencies 

 wdiich must have permeated the Grenville rocks during prolonged 

 periods. At the same time there may have been a contribution 

 of pyrite derived from magmatic sources. In the" field there seemed 

 to be strong evidence for this latter view in the general occurrence 

 of pyritiferous pegmatites associated with the ores, and it was 

 thought that these might be regarded as important bearers of pyrite, 



